OBJECTIVE: To explore the pattern of centrosome inheritance at fertilization and understand the motility and architectural changes necessary for the successful completion of fertilization in nonhuman primates. RESULTS Microtubule imaging has demonstrated that centrosome inheritance in nonhuman primates is paternal in origin, making the rhesus monkey an excellent model for examining human reproduction. To understand the motility and architectural changes necessary for the successful completion of fertilization, we have asked 1. What characterizes the organization of microtubules during fertili-zation in rhesus monkeys, and does it suggest the maternal or paternal inheritance of the centrosome? This information is key to understanding centrosome heredity, fundamental aspects of the motility leading to genomic union, and perhaps the evaluation and alleviation of infertility. 2. Is there evi-dence for a paternal centrosome contribution during polyspermy? These experiments will show whether polyspermy is lethal solely because of a genomic imbalance, or if supernumerary centro-somes are also problematic in primates. 3. Will parthenogenetically-activated oocytes organize bi-polar mitotic apparatus at the time of first division? If so, this would provide an indication that the oocyte contains all the necessary constituents for spindle formation, as well as provide information on the mode of centrosome inheritance. 4. What is the role of microtubules during rhesus fertilization? Does taxol treatment support the hypothesis that the sperm contributes the dominant, and perhaps sole, centrosome? Will zygotes recovering from microtubule inhibition form bipolar spindles in association with the male, but not female, pronucleus? We will address these questions through the use of microtubule inhibitors. 5. What are the dynamic properties of microtubules in maturing and mature rhesus oocytes? This knowledge may help clinicians evaluate at which stage of meiotic matur-ation human oocytes should be frozen for possible later fertilization. This research will advance the understanding of genomic union during fertilization in primates, a key step in reproduction. FUTURE DIRECTIONS We plan to explore microtubule dynamics during novel methods of assisted reproduction, such as intracytoplasmic sperm injection, in rhesus monkeys. KEY WORDS imaging, fertilization, motility and development, mitosis, cytoskeleton